1. Technical Field
The present invention relates to a sheet supply apparatus wherein sheets placed on a sheet plate are adsorbed onto an adsorbent surface by air and are fed out, particularly to a sheet supply apparatus wherein a space not exposed to separation air is formed on the lower side of the region to which the separation air is blasted to the sheets adsorbed onto the adsorbent surface, between the sheets placed on the sheet plate and adsorbent surface.
2. Description of the Prior Art
A pneumatic sheet supply apparatus has been used as a sheet supply apparatus for an image forming apparatus in a photocopier and other devices. In the pneumatic sheet supply apparatus, air is blasted on the lateral end faces of the stacked sheets so that a sheet is raised, and the raised sheet is adsorbed onto the adsorbent surface of a punched belt or the like equipped with an air inlet for drawing in air. Then the belt is driven and rotated so that the sheet is conveyed.
In such a pneumatic sheet supply apparatus, when two or more sheets that are stuck to each other have been adsorbed onto the adsorbent surface, it is necessary to use a separation mechanism for separating these sheets.
In a well known separation mechanisms for an air supply mechanism, air is blasted on the end of the adsorbed sheets, and the sheets are separated by the air inserted therebetween. However, separation is difficult in the case of thin plain paper and recycled paper. Blasting of air alone often fails to separate sheets, and the problem of multiple sheet feed has been raised in this conventional mechanism.
To assist the separation effect by air blasting, one of the techniques known in the conventional art uses protrusions from the adsorbent surface (Japanese Patent Application Publication No. Sho 61-254438). In this method, one topmost sheet to which the suction force is directly applied is adsorbed onto the adsorbent surface so as to wrap around the protrusions. On the other hand, the suction force is not directly applied to the sheets having been adsorbed by being entrained by the topmost sheet. Thus, these sheets are stopped at the position where they have come in contact with the protrusions, or are adsorbed on the adsorbent surface with gradual deflection. In this manner, more accurate separation can be achieved by using the differences in postures between the topmost sheet, and second and later sheets.